Printed circuit boards (PCBs) are widely used in the electronics industry for the manufacture of electronic assemblies. PCBs may be assembled from stacks of dielectric layers (sometimes called “prepreg” layers prior to assembly) and/or laminates or cores. A laminate or core may include at least one planar electrically insulating layer and conductive foils or films on one or both surfaces of the insulating layer. Some of the conductive films may be patterned, using lithographic techniques, to form conductive interconnects that are used to make electrical connections within circuits formed on the PCB.
The dielectric layers, conductive films (patterned or unpatterned), and laminates may be formed into a multi-layer, integral “board” structure by pressing together a stack of layers and curing the prepreg layers. In some cases, there may be 10 or more interconnect levels in a multi-layer PCB. When fully assembled, the circuits may include a variety of circuit elements soldered to or otherwise attached to the PCB. The circuit elements may include, e.g., resistors, capacitors, inductors, transistors, fuses, integrated circuits (ICs) or chips, trim pots, electro-acoustic devices, microelectromechanical devices (MEMs), electro-optical devices, microprocessing chips, memory chips, multi-pin connectors, and various types of sensors, etc. Some of the conductive films may be left substantially intact and may act as ground or power “reference planes.”
PCBs are routinely used in consumer electronics as well as custom applications. For example, PCBs may be used in smart phones to connect and enable data communication between processing electronics, signal transmitting and receiving electronics, and a display. PCBs may be used in laptops and personal computers for similar purposes. PCBs may be used in signal routers and data communication equipment. In such applications, large amounts of data and/or high-speed signals may be transmitted through interconnects of a PCB. Common insulating materials used in the manufacture of PCB dielectric layers support non-return-to-zero (NRZ) data transmission rates up to about 30 Gb/s. Because attenuation and speed of propagation of a signal along a trace depends on characteristics of the material surrounding that trace, more expensive, state-of-the art, high-performance insulating materials may be used to increase the transmission rates to nearly double that.